The present invention relates to an electronic device assembly, and more particularly to an electronic device assembly including a first substrate and a second substrate mounted on the first substrate.
An example of a conventional electronic device is disclosed in U.S. Pat. No. 5,203,075.
Referring to FIG. 10 of the above reference, a semiconductor device 43 is mounted on a flexible substrate 31. The flexible substrate 31 is connected to a substrate 13 via solder.
Referring to FIGS. 6 and 9 of the reference, a solder member 32 and a solder paste 27 connect the flexible substrate 31 and the substrate 13. Part of the solder member 32 is positioned in a through-hole provided in the flexible substrate 31.
The aforementioned structure has the following problems.
First, the solder connection is susceptible to failure because it is not protected from mechanical stress. Specifically, the solder connection is apt to fall off, be broken, or be short circuited with the adjacent solder connection. This problem becomes serious when a relatively heavy device such as a heat sink is mounted on the flexible substrate. The failure of the solder connection is also caused by thermal cycling (i.e., repetitive beating and cooling).
Second, the solder is further susceptible to failure because it is not protected from air humidity (e.g., the moisture in the air).
Third, it is difficult to control the gap precisely between the flexible substrate 31 and the substrate 13 because it is difficult to keep the flexible substrate 31 flat. If the gap between the flexible substrate 31 and the substrate 13 is uneven, the reliability of the solder connection decreases.